A device that allows boreholes to be isolated from the ocean water above the seabed and conditions in the hole to be monitored for long periods of time. CORK’s purpose is to provide a long–term seafloor observatory intended to allow a monitored and accessible borehole to return to its pre–drilling state. The CORK data logger can record temperature and pressure data for five years, and store it in memory for an additional five years until it can be retrieved via either a manned submersible or a ROV. The data is obtained by a string of sensors hanging from CORK at the bottom of the borehole. It also has fittings for recovering samples from inside the hole and allows fluid to be injected into the hole for certain kinds of tests.